Larger capacity and higher-speed transfer are eagerly requested in future for data reproducers such as an optical (magnetic) disk drive and a hard disk drive (HDD) represented by a DVD (Digital Versatile Disk) and MO (Magneto-Optical disk) continuously becoming higher density in recent years in the deversified information society. However, in the case of a recording medium for these data reproducers, a track interval becomes very narrow. Therefore, the quality of a reproduction signal is easily influenced by crosstalk and higher density is difficult.
To realize higher density by improving the quality of the reproduction signal, it is considered to detect and cancel crosstalk.
FIGS. 1 and 2 are illustrations showing examples of formats to be applied to a recording medium in order to detect crosstalk. FIG. 1 shows an example of a format which does not distinguish between crosstalks from both tracks adjacent to each other and FIG. 2 shows an example of a format which differentiates crosstalk from which of both tracks adjacent to each other.
In either of examples of formats in FIGS. 1 and 2, crosstalk detection areas 3 in which 1T continuous block and 4T continuous block are arranged on tracks 1_1, . . . , and 1_5 and block arrangement patterns between the 1T continuous block and the 4T continuous block are different between adjacent tracks in the crosstalk detection areas 3. Thus, when a beam spot 2 becomes off track in the crosstalk detection areas 3 in which the 1T continuous block and 4T continuous block are arranged, it is possible to detect the crosstalk generated in a reproduction signal.
In this case, sample data values (reproduction signals) reproduced from the 1T continuous block and 4T continuous block are described.
FIG. 3 is an illustration showing sample data values reproduced from the 1T continuous block and 4T continuous block.
The pattern “10101010” shown in FIG. 3 shows the data recorded in the 1T continuous block and the pattern “11110000” shows the data recorded in the 4T continuous block. These recorded data values are reproduced by a reproducing channel having the 1+D characteristic and become sample data values (reproduction signals) of “11111111” and “12221000”. Therefore, the reproduction signal from the 1T continuous block is a signal having an amplitude of 0 and a reproduction signal from the 4T continuous block has a large amplitude.
The examples of formats shown in FIGS. 1 and 2 respectively calculate a crosstalk value by measuring how many amplitude signals due to the 4T continuous block of adjacent tracks cause crosstalk in the 1T continuous block in which amplitude does not occur by using characteristics of the reproduction signals.
FIG. 4 is a conceptual view of crosstalk detection.
In the case of the reproduction signal 4_1 when there is no crosstalk, amplitude becomes 0 in the 1T continuous block. However, in the case of the reproduction signal 4_2 when there is crosstalk, an amplitude signal 5 is detected in the 1T continuous block and the amplitude signal 5 is crosstalk due to the 4T continuous block of adjacent tracks. Moreover, by comparing the amplitude of the 4T continuous block at the previous stage with a 4T continuous amplitude causing crosstalk, it is possible to measure the degree of crosstalk.
A technique which detects crosstalk in a test area on a recording medium in accordance with the principle of the crosstalk detection concept and applies offset to a beam spot position to a track (for example, refer to Patent Document 1) and a technique which forms a crosstalk detection area by using a prepit (for example, refer to Patent Document 2) are known.
(Patent Document 1) Japanese Patent Laid-Open No. 8-77627
(Patent Document 2) Japanese Patent Laid-Open No. 8-45080
However, it is difficult to obtain an accuracy which sufficiently improves a quality of a reproduction signal by the crosstalk detection according to the principle. Moreover, the capacity of a recording medium is lost by a value equivalent to a crosstalk detection area.
The quality of a reproduction signal is influenced also when the offset of a signal intensity or a gain defect of a signal occurs in a processing circuit which processes a reproduction signal other than the case of the crosstalk.